# Cosmic-Ray Propagation in Light of Recent Observation of Geminga

## TL;DR

Recent observations of Geminga suggest localized slow diffusion zones around pulsars, which impact cosmic-ray propagation models and could be common throughout the Milky Way, affecting interpretations of gamma-ray and positron data.

## Contribution

This paper introduces two-zone diffusion models that reconcile HAWC observations with cosmic-ray data, highlighting the significance of slow diffusion zones around pulsars.

## Key findings

- Two-zone diffusion models fit HAWC data well.
- Size of slow diffusion zones affects gamma-ray spectra.
- Implications for widespread slow diffusion pockets in the Galaxy.

## Abstract

The High Altitude Water Cherenkov (HAWC) telescope recently observed extended emission around the Geminga and PSR~B0656+14 pulsar wind nebulae (PWNe). These observations have been used to estimate cosmic-ray (CR) diffusion coefficients near the PWNe that appear to be more than two orders of magnitude smaller than that typically derived for the interstellar medium from the measured abundances of secondary species in CRs. Two-zone diffusion models have been proposed as a solution to this discrepancy, where the slower diffusion zone (SDZ) is confined to a small region around the PWN. Such models are shown to successfully reproduce the HAWC observations of the Geminga PWN while retaining consistency with other CR data. It is found that the size of the SDZ influences the predicted positron flux and the spectral shape of the extended $\gamma$-ray emission at lower energies that can be observed with the {\it Fermi} Large Area Telescope ({\it Fermi} LAT). If the two observed PWNe are not unique, then it is likely that there are similar pockets of slow diffusion around many CR sources elsewhere in the Milky Way. The consequences of such picture for Galactic CR propagation is explored.